Graphene is a monolayer thin-film having a planar honeycomb structure, achieved through chemical bonding of carbon atoms with a sp2 hybrid orbital. Since graphene has very high conductivity and is flexible, it is receiving attention as an alternative to inorganic material such as silicon, which is fragile and easily breakable.
Methods of synthesizing graphene include mechanical or chemical peeling, chemical vapor deposition, epitaxial synthesis, organic synthesis and the like. In particular, chemical vapor deposition is very suitable for the mass production of large, high-quality graphene layers.
In its current state, chemical vapor deposition is problematic because the metal catalyst for growing graphene is directly exposed to flowing gas and the extent of growth of graphene may vary depending on the concentration of material gas. In the case where the concentration of material gas is too low, it is difficult to synthesize graphene.
Furthermore, chemical vapor deposition causes graphene to grow at a high temperature. In this case, as the grains of the metal catalyst grow, the grains may come into contact with each other at the grain boundary. It is easy to form multilayer graphene at the grain boundary of the metal catalyst, and the multilayer graphene may deteriorate the light transmittance of the final graphene sheet. Specifically, because the grain size of the metal catalyst is small and many grain boundaries are formed, the area in which synthesized graphene takes a multilayer form is likely to increase, consequently decreasing the light transmittance of graphene. The preparation of graphene using conventional chemical vapor deposition suffers from low transmittance of synthesized graphene attributable to the metal catalyst having a small grain size with many grain boundaries. Hence, there is a need for a graphene synthesis method in which the grain size of the metal catalyst is increased and the scale of the grain boundary is reduced, thus suppressing the growth of multilayer graphene so as to increase light transmittance.
In the conventional synthesis of graphene, graphene is synthesized under a condition such that the surface of a metal catalyst (e.g. Cu), useful for the synthesis of monolayer graphene, is exposed in a deposition machine. As such, upon chemical vapor deposition at a temperature approximately as high as the melting point of the catalyst (e.g. 1,040° C. for Cu), the surface of the catalyst is undesirably melted.